1. Field of the Invention
The present invention relates to a heat activation method for a thermosensitive adhesive label comprising a support, and a thermosensitive adhesive layer which is formed on the support without a liner (i.e., a disposable backing sheet) and is not adhesive at room temperature, but can be made adhesive with the application of heat thereto.
The present invention also relates to an apparatus for heat-activating the above-mentioned thermosensitive adhesive layer of the thermosensitive adhesive label and a label printer capable of printing images on the thermosensitive adhesive label and heat-activating the thermosensitive adhesive layer thereof.
2. Discussion of Background
Recently, a recording label, in particular, a thermosensitive recording label has been used in a wide variety of fields, for example, in the system of point of sales (POS). In most of the above-mentioned conventional thermosensitive recording labels, a pressure-sensitive adhesive layer is generally provided on the back side of a thermosensitive recording layer, so that the label is stored in such a fashion that a liner (i.e., disposable backing sheet) is attached to the pressure-sensitive adhesive layer.
Such a thermosensitive recording label is useful, but it has some shortcomings. For instance, the liner must be discarded after being released from the adhesive layer. Therefore, consideration must be given to the problem of waste disposal from the ecological viewpoint. In addition, the manufacturing cost is increased because of not only the cost of the liner itself, but also expenses involved by the treatment of the liner.
To solve the above-mentioned problems, there are proposed recording labels without a liner. For instance, as disclosed in Japanese Laid-Open Utility Model Applications 59-43979 and 59-46265 and Japanese Laid-Open Patent Application 60-54842, it is proposed to employ an adhesive layer comprising a pressure-sensitive adhesive in micro-capsule form, and to provide a releasing agent layer on the surface of the recording label, opposite to the pressure-sensitive adhesive layer side so that the recording label may be stored in the form of a roll. By the above-mentioned conventional proposals, however, sufficient adhesion is not generated in the pressure-sensitive adhesive prepared in the form of micro-capsules, and printing cannot be carried out on the surface of the label when the releasing agent layer is provided thereon.
Furthermore, there is proposed a thermosensitive adhesive label comprising a thermosensitive adhesive layer with no liner being attached thereto, as disclosed in Japanese Patent Publication 60-24011 and Japanese Utility Model Publication 60-25371. When such a recording label comprising a thermosensitive adhesive layer is employed, it is necessary to heat-activate the thermosensitive adhesive layer by the application of heat thereto so as to make the thermosensitive adhesive layer sufficiently adhesive.
There is proposed a heat activation method for the above-mentioned thermosensitive adhesive layer, as disclosed in Japanese Patent Publication 60-24011. According to this heat activation method, the thermosensitive adhesive label is transported along a heat-resistant transporting belt with the thermosensitive adhesive layer of the label in contact with the surface of the transporting belt. In this case, the transporting belt is heated by a heater which is situated on the opposite side to the thermosensitive adhesive label with respect to the belt. The heat-resistant transporting belt is heated by the heater, and the thermal energy thus generated is transmitted to the thermosensitive adhesive layer of the label, thereby achieving the heat-activation of the thermosensitive adhesive layer.
However, the heat-activating efficiency is poor when the thermosensitive adhesive label is heat-activated by the above-mentioned heat activation method. This is because the thermosensitive adhesive label is just put on the transporting belt, so that the thermosensitive adhesive label does not closely adhere to the transporting belt.
According to Japanese Utility Model Publication 60-25371, there is disposed a hot-air generating apparatus at a predetermined distance from a transporting belt. The thermosensitive adhesive layer of the thermosensitive adhesive label is heat-activated in such a manner that the thermosensitive adhesive label is exposed to hot air generated by the above-mentioned hot-air generating apparatus while the label is transported along the heat-resistant transporting belt, with the thermosensitive adhesive layer in contact with the transporting belt.
This heat activation method employs hot air, so that the safety of the heat activation apparatus for the thermosensitive adhesive label cannot be ensured, and the heat activation apparatus cannot be made compact because the heat activation apparatus must be equipped with the hot-air generating mechanism.
Furthermore, in the above-mentioned heat activation methods as disclosed in Japanese Patent Publication 60-24011 and Japanese Model Utility Publication 60-25371, for the purpose of smoothly separating the heat-activated thermosensitive adhesive label from the transporting belt, the transporting belt is bent with forming a sharp angle at the position where the thermosensitive adhesive label is separated from the transporting belt. Such a bend of the belt will induce deterioration soon. In addition, a metal which is most suitable for the transporting belt because of its high thermal conductivity cannot be used as the material for the transporting belt. This is because it is hard to bend a metallic belt with forming an acute angle without causing the deterioration.